The present invention relates generally to a seat belt warning system and more specifically to a seat belt reminder system comprising a seat occupancy sensor for detecting an occupancy of a vehicle seat and a seat belt sensor for detecting whether a seat belt is fastened or not.
Today's automotive safety standards require automotive vehicles to be equipped with seat belt reminder systems for reminding a vehicle passenger to fasten the seat belt associated to the occupied vehicle seat. While until now, those seat belt reminder systems where mainly associated with the front seats of the vehicle, future standards will require that also rear seat be equipped with such seat belt reminder systems.
Seat belt warning systems typically comprise a seat occupancy sensor associated with a vehicle seat for determining the presence of an occupant on the respective seat and for generating a signal indicative of such presence, and a seat belt fastening detector for determining a seat belt usage condition and for generating a signal indicative thereof. A control unit then uses the signals of the seat occupancy sensor and the seat belt fastening detector in order to deter-mine whether the actual seat occupancy would require a non-fastened seat belt to be fastened and, if this is the case, to issue a corresponding warning signal.
The seat occupancy sensors usually comprise pressure sensing devices integrated in the respective passenger seat for detecting a pressure induced by the presence of a passenger into the seat. The pressure sensing devices, as e.g. disclosed in DE-A-42 37 072, comprise a plurality of individual force sensors, which are connected in a suitable manner to a control unit designed for measuring a pressure depending electrical property of said individual pressure sensors. These occupancy sensors have proven to be very reliable and well adapted to the detection of seat occupancy.
The seat belt fastening detectors typically comprises mechanical or magnetic buckle switches for detecting, whether a latch of the seat belt is inserted into the seat belt buckle. One such buckle switch is e.g. disclosed in U.S. Pat. No. 5,871,063. As an alternative to the buckle switches, seat belt detectors have been proposed which generate a buckled/unbuckled signal based on the tension in the seat belt.
One drawback of the known seat belt warning systems lies in the fact, that the seat occupancy sensor and the seat belt fastening detector have to be physically connected to the control unit by means of connection wires in order to be functional. This need for physically connecting the sensing device to the control unit however causes problems especially in modern cars equipped with a flexible seating system with removable and/or displaceable back seats.